Our work focuses on the characterization of the major histocompatibility complex (MHC); namely, the B locus, of chickens. In this connection we propose to determine the mechanism of the immune responses to synthetic polypeptides and other antigens which we have reported to be associated genetically with the MHC. In addition, we propose to continue our study on the structural and genetic analyis of chicken immunoglobulin allotypes. Efforts will be made to determine whether the phenotypic polymorphism (allotypes) we have observed reflects extensive genotype diversity generated by repeated intragenic recombination occurring between the Fd region allotypes and the papain-sensitive region allotypes of the S7 immunoglobulin H chain. BIBLIOGRAPHIC REFERENCES: Class, amounts and affinities of anti-dinitrophenyl antibodies in chickens. 1. Production of S7 and S17 antibodies of equal affinity by intravenous injection of antigen. Yamaga, K. and Benedict, A. A., J. Immunol. 115: 750, 1975. Class, amounts, and affinities of anti-dinitrophenyl antibodies in chickens. II. Production of a restricted population of high affinity S7 antibodies by injection of antigen emulsified in adjuvant. Yamaga, K. and Benedict, A. A. J. Immunol. 115: 759,1975.